1. Field of the Invention
The present invention related generally to medical treatment devices, and, more particularly, to a counterpulsation treatment apparatus for treating reduced cardiac output in patients, specifically, for treating occlusions in coronary arteries.
2. Description of the Related Art
External counterpulsation has developed as a means of treating reduced cardiac output and circulatory disorder stemming from disease. Counterpulsation treatment involves the application of pressure, usually from distal to proximal portions of a patient's extremities, where such application is synchronized with heart rhythms. The treatment augments blood pressure, typically increasing pressure during the diastolic phase of the heart, as such treatment is known to relieve and treat medical conditions associated with reduced cardiac output. Clarence Dennis described an early hydraulic external counterpulsation device and method of its use in U.S. Pat. No. 3,303,841 (Feb. 14, 1967). Dr. Cohen, in American Cardiovascular Journal (30(10) 656-661, 1973) described another device for counterpulsation that made use of balloons which would sequentially inflate and deflate around the limbs of a patient to augment blood pressure. Similar devices using balloons have been described in Chinese patents CN 85200905 (U.S. Pat. No. 4,753,226); Chinese patents CN 88203328, and CN 1057189A.
A series of Zheng patents, including U.S. Pat. No. 4,753,226 (Jun. 28, 1988), U.S. Pat. No. 5,554,103 (Sep. 10, 1996), and U.S. Pat. No. 5,997,540 (Dec. 7, 1999) disclose counterpulsation devices employing sequential inflation of balloon cuffs around the extremities, wherein the cuffs are inflated by a fluid. All three Zheng patents disclose an external counterpulsation device where a series of air bladders are positioned within a rigid or semi-rigid cuff around the legs. The bladders are sequentially inflated and deflated with fluid, such that blood pressure is augmented in the patient. The Zheng '103 and Zheng '540 patents provide for cooled fluid and for monitoring of blood pressure and blood oxygen saturation; however, both retain a similar mechanism dependent on compression of fluid such as air. The Zheng '540 patent modifies the shape of the air bladder and cuffs, but retains a similar mechanism requiring rapid fluid distribution, influx and efflux through balloons in the cuffs.
U.S. Pat. No. 3,734,087 to Sauer et al., U.S. Pat. No. 3,786,802 to Hagopian, et al. and U.S. Pat. No. 3,835,845 to Maher, all disclose a system that utilizes a hydraulically actuated rod to move a platen from a resting position to a position placing pressure on a liquid filled bladder. Liquid is either removed or added to the bladder over several cycles in order to regulate the pressure against the patient's legs. This procedure of regulating the pressure output of the invention is inefficient due to the time and imprecision involved in making the necessary adjustments.
Bladders are also utilized to regulate the pressure exerted on the subject's extremities in U.S. Pat. No. 3,866,604 to Curless, et al. and U.S. Pat. No. 3,654,919 to Birtwell. As stated above, this procedure is ineffective and imprecise. Britwell further teaches the use of a hydraulically driven piston to switch between a suction zone and a hydraulic zone. In a first position, liquid is released into the bladder system affixed circumferentially around the subject's legs. In an opposite second position, the liquid is removed. This invention does not allow for quick and precise adjustments of the resulting pressure and the piston is not adjustable to a plurality of positions in order to more finely tune the pressure output.
There are several deficiencies with prior pulsation treatment devices. First, the required circuitous movement of fluid through the apparatus causes a delayed response to changes in pressure settings for the balloons or air bladders. Second, there is also a consequent inability to manipulate action of the cuffs with a high degree of precision. Third, many of the prior art devices require a relatively heavy and noisy compressor. Fourth, the prior devices lack portability due to their large size and weight, and their reliance on a compressor. There are also deficiencies in some of these devices with regard to patients being bounced up and down while undergoing pulsation treatment.
Electromechanical solenoids were typically used to actuate the prior art designs in part due to their relative ease of installment as opposed to pneumatic or hydraulic actuators. Typically solenoids are also utilized for their quick operation. U.S. patent application Ser. No. 11/420,133 to Michael Lewis, the inventor herein, utilizes an electromechanical actuator comprising a solenoid that will operate on a 120-volt source of electric power. While this particular type of actuator is effective, a hydraulic actuator will prove to be more powerful and less prone to the typical wear seen in electrical components.
Hydraulic actuators are ideal for applications requiring precise control and smooth motion. Utilizing hydraulic actuators will allow for a greater plurality of adjustments in the tension of the cuff system due to the ease of regulating the pressure exerted on the hydraulic actuator itself. These types of minute adjustments are not as easily obtainable when utilizing an electromechanical actuator. The solenoids typically used in electromechanical actuators are better equipped to fluctuate from a fully open position to a fully closed position. While it may be possible to generally operate between these two extremes, the resultant operation will not be as fine tuned as when a hydraulic actuator is utilized.
Hydraulic actuators require less treatment table space because the actuators themselves are relatively smaller and less bulky than their electromechanical counterparts allowing for a relatively smaller frame. Hydraulic actuators produce less heat as well preventing premature shut downs due to overheating, which allows for extended use. Further, the hydraulic system's accumulator stores energy while the actuator is stationary which is a great advantage when the actuators are used intermittently, as in the present invention. A further benefit is the ability for several hydraulic actuators to share a single pump. This ability to operate several actuator from a single pump unit can result in lower costs per treatment as compared to electromechanical systems. Finally, the pressure generated from a hydraulic system can be maintained at a constant level without the need for signification additional energy.
A need therefore exists for a pulsation treatment apparatus that provides a rapid response to changes in applied pressure settings, and that permits control of cuff pressure with an even higher degree of precision than with an electromechanical actuator. Preferably, such a treatment apparatus will not require fluid filled balloons or air bladders and will not subject the patient to undesirable or unnecessary movement.